The present invention relates to an apparatus and a method of observing surface configurations by using an electron beam, and especially provides an apparatus and a method by which observation of either configurations of the bottom of a deep hole or residues therein, used frequently in semiconductor processes, can be permitted.
The scanning electron microscope, in which an electron beam is scanned on a specimen and secondary electrons generated from the specimen are detected, has been utilized widely in the fields of biology and engineering. Especially, in the semiconductor industry, high-integration formation has advanced and as a result, inspection based on optical microscopes has become impossible, and the utilization of the scanning electron microscope has been promoted. In a scanning electron microscope used for semiconductors, it is conventional to use an electron beam of low energy of 1 keV or less in order to avoid charging on insulators.
In the semiconductor industry, the scanning electron microscope is utilized for not only inspection of appearance of completed semiconductors but also inspection in mid-course of the manufacturing process. For example, it is used for inspection of appearance, inspection of dimension and inspection of through-holes in mid-course of the process.
As a result of the advancement of high-integration formation of semiconductor devices, it has become impossible for the method using the conventional scanning electron microscope to inspect openings of through-holes.
Referring to FIG. 2, problems encountered in observing a deep hole with the conventional scanning electron microscope will be described. FIG. 2 shows a case where a primary electron beam 1 of low energy irradiates a flat portion and a hole 3 of a specimen. Thanks to the absence of any obstacles, almost all of the number of secondary electrons 2 generated at the flat portion can be detected. Similarly, reflection electrons concurrently discharged can also be detected. In the case of irradiation of the hole 3, however, generated secondary electrons 2 impinge on the side wall of the hole 3 and consequently cannot escape from the hole 3 to the outside. The energy of reflection electrons is higher than that of secondary electrons but is not so high that the reflection electrons can penetrate through the side wall, and the reflection electrons are thus blocked by the side wall.
The present invention is further concerned with a method for displaying a scanning image of a specimen and an apparatus therefor. Examples of such specimens are devices and parts as represented by a semiconductor device, a photomask substrate inclusive of a multi-layer structure mask such as a phase shift mask, a display device such as a liquid crystal device or a CCD, a wiring board, a memory medium such as an optical disc, metal or polymer materials, cellular tissues and other living bodies.
Additionally, both intermediate products and finished goods are considered specimens for the purposes of the invention. The present invention handles these objects and is effective for use in observation, inspection, measurement and analysis of them or in monitoring techniques during treatment of specimens.
By way of example, in the field of observation of a fine structure of a specimen, of a scanning microscope using an electron beam having an energy level of several hundreds of eV to several tens of keV, and a transmission-type electron microscope using an electron beam of several tens of keV to several MeV, have been used for imaging a specimen and displaying the image on a specimen image display apparatus. Specimen image display techniques using the above electron microscope techniques are described in the literature; see, for example, "Fundamentals and Applications of Scanning Electron Microscope", originally edited and twice published by Kyohritsu Shuppan Kabushiki-Kaisha, May 25, 1985.
Disadvantageously, however, the conventional techniques described above have encountered difficulties in performing high-resolution or non-destructive observation of a surface structure having large unevenness or precipitous unevenness, and of an internal structure of a specimen.